This invention relates to high voltage feed-through bushings in general and in particular to those types of bushings used with circuit breakers.
Circuit breaker devices of the type containing sulfur hexafluoride gas (SF.sub.6) can contain a measureable quantity of hydrofluoric acid. The constant arcing of the circuit breaker electrodes provides sufficient energy to dissociate the SF.sub.6 gas and, in the presence of moisture, generate hydrofluoric acid. When bushings are used as high voltage feed-throughs for SF.sub.6 circuit breakers, a material other than porcelain or glass must be employed due to the corrosive effects of the hydrofluoric acid on the porcelain and glass materials. One material which is an effective substitute for porcelain in SF.sub.6 circuit breakers is epoxy resin. The hydrofluoric acid within the breaker has no deleterious effect on the epoxy material.
The hydrofluoric acid within the breaker also has a deleterious effect on the rubber gaskets used to provide a gas-tight connection between the bushing and the breaker and between the busing housing and the bushing bottom high voltage terminal. Materials which were found to be resistive to hydrofluoric acid were found to be ineffective materials for use as gaskets due to high gas permeability. Gaskets made from hydrofluoric acid-resisting materials allowed the SF.sub.6 gas to leak from the breaker.
The purpose of this invention is to provide methods and materials for forming gas-tight seals between epoxy bushings and SF.sub.6 circuit breakers which are corrosive resistant to hydrofluoric acid and are impermeable to sulfur hexafluoride gas.